Milling screw threads



G. RICHARDS, I.. N. BURT, AND I. E. FREEBORN.

MILLING scREw THREADS.

APPLICATION FILED FEB. I, IIZI.l AQYQ, Patented Aug. 29, 1922.

3- SHEETS-SHEET I.

G. RICHARDS, L. N. BURT, AND l. E. FREEBORN.

MILLING. SCREW THREADS. APPLICATION FILED FEB. I, 1921.

1,427,169, Patented Aug. 29, 1922.

3 SHEETS-SHEET 2.

G. RICHARDS, I.. N. BURT, AND I. E. FREEB'ORN. MILLING SCREW THREADS.

APPLICATION FILED FEB. I, 192|.`

@A2751 @9, Patented Aug. 29., 1922.

3 SHEETS-SHEET 3.

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parte@ stares rea-raar GEORGE RICHARDS mvp LESLIE, Nevin/fair i'a'ii'r, Loiuiiiitniiii J'Arimsniiwaai FREEBORN, orWALTHaMsToW, ENGLAND? Mimmo' scanw THREADS.

ratelrtelfi artig. 2a, tele2;

llllgmll). i Sp'ecficatioli vof Letters Patent.

JAMES EDWARD' vlTRprenoms,

original application inea Aprile, 1920,seria1 1", 1921.

TovlaZZ whomc't may concer/lt.'

:Be it known that we, GEORGE RrcHARDs, a citizen of the United States, and LESLIE NnwMANBURT, a subject. otthejKing of Great Britain and Ireland, both residing at The Outer Temple, of Westminster,vy London, y En, gland, 4Land a subjectoi'. the King of Great Britain and lreland,residing at' 2 Elmsdale Road, Walthamstow,7 in the county of Essex, England', have invented new and useful Improvements` in Milling Screw Threads, of which the following isa specification. ,v f

kThis invention kis the subject of a,l divisional application from Ser. No. `372315, filed'Sth April, 1920, and relates 'to improved apparatus. for cutting screw-threads -with' theaidof what are known as hob's; that` is to, say,rotary'cuttersiwherein the cutting' teethfollo-w spirallines having' a pitch corresponding with that'of the thread to be formed. It has hitherto been the practicey toimp'art to the' hob and to the `work-'piece the same' rotative speed,`but neither partakes of any axial movement. Under such conditions, itiisnecessary to make special' provisionl for the elimination of Ja'ce'ts, which' result from the cutting ,teethV coming successively into operation upon the work at they same points in successive revolutions. `There is, more` A over, the objection that theportion' of the work-piece threaded is restricted in' length toftha'tA of th'e'hob. A. further ,objection is that, when using a multiple-thread, hob, dif-y ficulties'occur in shaping the toothed thread on the hob, in such a. manner as' to cut, in' the" work, a thread'of the Vcorrect shape.

With' aview to avoiding' these objections, we mount the hob-spindle in a frame 'capable of being canted; such frame being mounted on` ai' slide, so as to adm-it of the hob being advanced laterally; towards the workpiece with a view to cutting the' thread in the latter to the required depth. The saidslide is in turn mounted on asaddle, adapted to be traversedmpon the be'd of the machine, and is: provided with a screw ot" predetermined pitch 'for effecting such movement.' When the hob-spindle is tilted in a Vvertical plane, and when ertreme` accuracy is require in the form ot the thread cut,'the surface ot 222 Strand, in the city' No.'372`,'315. ,Dv'd'ed'ad this application iiledFehriiary Serial No. 441,666.

the .heb isi-made slightly in a lolig'f` tudi'nal direction, or, vfor internal work,

slightly barrel-shaped.

he work-spindle, which is the headstock of the machine, is inigearwith the hob-spindle; these two spindles revolveefcontrery t0 the usuel. practice at slight.. lydiiferent speeds; The workspindle isalso in gearwith the screw which operatesthe tnaverseslidc, ythe pitch of the said screw, .0r thegearing, whereby-it,v is* driven, being proportioned yto the diilerence between, the rohtative speedlof the work-spindle and `that of the hob-spindle.

Under such conditions, by reason, of the axial advance of the hob in rclationto'the, work, therotative speed of the-,former,'or otthe latter, being varied to suit, we are able to screw-threadportions ofqthe ,workv the length ofI whichI considerably exceeds that ot the hob. Moreover,l as workthreads` out by the leading hob-threadSrlre sulosequently operated on bythe following hob# threads, any facets ormedby`r the leading hoh-threads become eliminated.,1

The provision of substantial and l`rigid support for the` cutterfspindle is offir'npor'a tance, and is facilitated by the employment ofataperhob. l A. 1,' .L

Apparatus adaptedor use'. in .carrying our inventioninto effect isillustra'ted in the; accompanying drawings, whereofl Fig. ALis' a` vertical section of ,partof the gearemp-loyed to drive' the cutter spindle, Figi2lbeing ar partly diagrammatic endelevation illustrating. ,gears arranged between the'l latterr dos 7, are respectively a sectional plan, andza l front elevation showing the general arrange'-k mentl of the apparatus, whilst' Fig! 8' is; a` diagrammatic view illu'strating` certain furith gearing hereinafter described. f.

wayyof asuitably arranged diil'erential-l gear., the rotative movement which is impartedfto the carriage traversing mechanism, the hob may be speedefd up, or retarded, according to the direct on of travel, in such '.-a marmer transmitting to the cutter-spindle';-.by.

a saddle 5. In a suitable bracket 51 mounted' upon the worm-wheel a1 and able to revolve with the latter, is arranged a short shaft c v whereon are vfreely mounted two similar bevel-wheels c1, c1, which mesh with a bevelwheel al, mounted on a shaft flwhereot the outer extremity carries a spur-wheel. d2.

The bevel-wheels' 01,61, also mesh with a further bevel-wheel e, mounted upon a crosssh-aft f, from which the cutter-spindle is driven. From the back-shaft a driving the worm-wheel al', the drive is transmitted to the cross-shaft f, by way of the bevel-wheels c1, 01, meshing with the bevel-wheel d, and thence tov the bevel-wheelv e, which is fast upon the cross-shaft f; the bevel-wheel d remaining locked when, asin cutting a short length of screw-thread, no traverse of the hob is eected. Y

The traverse of the saddle Z), and hence that of the'hob, is'effected by transmitting the power supplied bythe back-shaft a through suitable'gears g, g1, g2, as shown in Fig. 2, todrive the worm-shaft 7L at a suitable speed; provision being ymade for throwing these gears into and'out of engagement.' The worm-shaft 7L, carries a worm h1 which meshes with a worm-wheel k2, the boss of which is internally screwthreaded to form a nut adapted to traverse the lead-screw j which is held against rotation. The outer extremity of the wormshat t carries a spur-wheel 72,3, which, as; shown in Fig. 3, meshes with the spur-wheel i d2, through one or more suitable idlers, such adapted to produce when hand, as described as als; provision being, moreover, made for varying the saidv spur-wheels and idlers in order to establish different speed ratios threads of the particular form required.

Short lengths of thread, less than or equal tothe hob in length may thus be out without any vendwise motion of the saddle j the p feed-'drive is, by any suitable means, thrown 'out of engagement; but should a creep7 motion be required in these short lengths of thread, a'hand-lever may be attached tothefront endI of the worm-shaft 71;, and the required creep vbe produced by v and illustrated in the specification to the co-pendingfapplication. ofv George Richards, filed 5th February, 1917,' Ser. bld-146692.

san alternative, the lead-screw may be driven in conjunction with similar gear Vto produce the same elect; or the lead-screw may be driven direct, producing a different speed ratio from that of the hob, as in Fig. 5. j y

ln order to permit ot the cutter-spindlev bein rigidly supported, a taper hob may be emp oyed, so as to permit of the carriage assuming an angular position `in relation tol the work;` thus providing the necessary clearance for a substantial and steady car-A riage, as shown in'Figs. 4t and 5.'

To enable the hob to assume the correct position for the teeth to cut in the path of the helix angleof the thread on the work, the saddle Z) is, as shown in ig. 6, mounted on a bed la and carries a cross-slide Z which maybe moved laterally to obtain various depths of thread by means of a screw-spin-A dle m.

The cross-slide b carries a pivotally mounted carriage n, arranged vertically in relation to the bed and adapted to rotate about the centre 701, as shown diagrammatically in F ig. 8, in order to adjust the axisl ot the hob to any angle required.

The carriage a which supports thefcutter-` spindle p may, by means of the screw o and hand-wheel 01,' be adjusted vertically on slides carried by the pivotally mounted carriage n, as illustrated in Fig. 7. The drive v:tor the cutter-spindle p is imparted, as

shown in Fig. 6, from` the cross-shaft 7 through suitable spur-wheels 01, p?, p3, p4,

whereof the last indicated is free to revolve about the centrekl'whereonthe spur-wheel P3 is mounted.

Thespur-wheels p1,'p2, p3, are mounted in the cross-slide Z; the spur-wheel'p1 being tree to slide upon a spline along-the cross-l shaft f. f'

The spur-wheel .p4 drives the worm-shaftr shown in Fig. 6, and thence, by way of the worm r1, and the worm-wheel s1, the vertical shatt s upon which the worm-wheel t is free to slide vertically upona spline, as shown in Fig. 7 the cutter-spindle p being driven by means of a worm-wheel :amounted at its extremity and meshing with the worm-wheel t. l

Under such conditions,the hob-teeth may be adjusted to cut along any angle required to conform with the helix of any particular thread. -Furthermore, on reaching the end of the thread, when using a parallel'hob', thecarriage n may be fed downwards to finish those threads, which, by reason of the end of the hob being canted above the workcentre, have been left unfinished. 'i We claim :--y

l. In a screw-thread milling machine wherein a cutter of the hob type is-em'- ployed, the combination, with a transverse .,lide, of a carriage rotatably mounted upon 'f 2. In a screw-thread milling machine wherein a cutter of the hob type is em- 10 wherein a cutter of the hob type is employed, the combination, with a saddle-travployed, the combination, With a outter-spin ersin Worm-shaft, of a cutter-spindle drivdle and its carriage, of a Worm-shaft, carrying s aft, the tWo shafts being coupled toing a Spur-Wheel meshing with and revogather by Way of a differential speed-gear. luble about a spur-Wheel mounted upon the centre about which the cutter-spindle-ear- GEORGE RICHARDS. riage is rotatable. LESLIE NEWMAN BURT.

3. In a screw-thread milling machine JAMES EDWARD FREEBORN. 

